DESCRIPTION (Applicant's Abstract): Successful surgical treatment of intractable epilepsy requires accurate presurgical localization of cortical seizure foci. Presurgically, cognitive assessment contributes to lateralization and localization of cortical dysfunction associated with epileptogenic tissue and assists prediction of postoperative abilities. In certain cases, cortical mapping of cognitive functions is required to prevent postoperative decline. Visual object naming is a major component in presurgical assessment of verbal skills and is widely utilized during cortical mapping to prevent postoperative language dysfunction in patients with seizures arising near language cortex. However, many temporal lobe epilepsy (TLE) patients who complain of word finding difficulties and show deficits in conversation show no deficits on object naming tasks. Furthermore, postoperative word finding deficits can arise or become more severe despite utilization of visual naming tasks during language mapping. These observations challenge the validity of using visual naming 1) to detect word finding difficulties and thereby infer localization of seizure foci and 2) to help prevent postoperative language decline. Preliminary findings suggested that auditory naming was significantly more sensitive to word retrieval deficits in left TLE (i.e., language dominant, LTLE) patients than was visual naming. This discrepancy may reflect differences in the cognitive operations underlying word retrieval during object naming and during speech. In addition, preliminary observations during cortical mapping using visual and auditory naming tasks indicated that these functions were differentially impaired by stimulation at a given cortical site, suggesting they reflect different aspects of language processing.